CN114275765A - Lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material and preparation method and application thereof - Google Patents
Lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material and preparation method and application thereof Download PDFInfo
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical group [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 title claims abstract description 89
- 229910021393 carbon nanotube Inorganic materials 0.000 title claims abstract description 87
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 74
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 74
- 239000002131 composite material Substances 0.000 title claims abstract description 43
- 229910052799 carbon Inorganic materials 0.000 title claims abstract description 32
- 239000011258 core-shell material Substances 0.000 title claims abstract description 25
- 238000002360 preparation method Methods 0.000 title claims abstract description 15
- 229910001386 lithium phosphate Inorganic materials 0.000 claims abstract description 93
- TWQULNDIKKJZPH-UHFFFAOYSA-K trilithium;phosphate Chemical compound [Li+].[Li+].[Li+].[O-]P([O-])([O-])=O TWQULNDIKKJZPH-UHFFFAOYSA-K 0.000 claims abstract description 93
- 239000002041 carbon nanotube Substances 0.000 claims abstract description 57
- 239000002245 particle Substances 0.000 claims abstract description 56
- 239000000463 material Substances 0.000 claims abstract description 48
- 238000010438 heat treatment Methods 0.000 claims abstract description 21
- 229920000642 polymer Polymers 0.000 claims abstract description 21
- 239000013589 supplement Substances 0.000 claims abstract description 19
- 229920001690 polydopamine Polymers 0.000 claims abstract description 15
- 238000000227 grinding Methods 0.000 claims abstract description 8
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 claims description 36
- 239000000243 solution Substances 0.000 claims description 35
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 32
- FYFFGSSZFBZTAH-UHFFFAOYSA-N methylaminomethanetriol Chemical compound CNC(O)(O)O FYFFGSSZFBZTAH-UHFFFAOYSA-N 0.000 claims description 19
- 238000003756 stirring Methods 0.000 claims description 19
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 16
- 238000000498 ball milling Methods 0.000 claims description 15
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 15
- CTENFNNZBMHDDG-UHFFFAOYSA-N Dopamine hydrochloride Chemical compound Cl.NCCC1=CC=C(O)C(O)=C1 CTENFNNZBMHDDG-UHFFFAOYSA-N 0.000 claims description 14
- 229960001149 dopamine hydrochloride Drugs 0.000 claims description 14
- 238000001035 drying Methods 0.000 claims description 14
- 238000000034 method Methods 0.000 claims description 11
- 238000002156 mixing Methods 0.000 claims description 9
- 238000001291 vacuum drying Methods 0.000 claims description 8
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 7
- 239000007864 aqueous solution Substances 0.000 claims description 7
- 239000008367 deionised water Substances 0.000 claims description 7
- 229910021641 deionized water Inorganic materials 0.000 claims description 7
- 239000000178 monomer Substances 0.000 claims description 6
- 239000007791 liquid phase Substances 0.000 claims description 4
- 239000012300 argon atmosphere Substances 0.000 claims description 2
- 238000005119 centrifugation Methods 0.000 claims description 2
- 238000006243 chemical reaction Methods 0.000 claims description 2
- 238000006116 polymerization reaction Methods 0.000 claims description 2
- LENZDBCJOHFCAS-UHFFFAOYSA-N tris Chemical compound OCC(N)(CO)CO LENZDBCJOHFCAS-UHFFFAOYSA-N 0.000 claims description 2
- 238000004140 cleaning Methods 0.000 claims 1
- 239000003575 carbonaceous material Substances 0.000 abstract description 10
- 229910021385 hard carbon Inorganic materials 0.000 abstract description 8
- 239000000126 substance Substances 0.000 abstract description 4
- 238000000926 separation method Methods 0.000 abstract description 2
- 229910019142 PO4 Inorganic materials 0.000 abstract 1
- 239000010452 phosphate Substances 0.000 abstract 1
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 12
- 238000005406 washing Methods 0.000 description 11
- 229910052786 argon Inorganic materials 0.000 description 6
- 238000001816 cooling Methods 0.000 description 5
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 3
- 239000007772 electrode material Substances 0.000 description 3
- 229910001416 lithium ion Inorganic materials 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 239000002033 PVDF binder Substances 0.000 description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 2
- 239000011889 copper foil Substances 0.000 description 2
- 239000001301 oxygen Substances 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 229920002981 polyvinylidene fluoride Polymers 0.000 description 2
- 239000002109 single walled nanotube Substances 0.000 description 2
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 description 1
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 description 1
- 229910001290 LiPF6 Inorganic materials 0.000 description 1
- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 1
- 230000001154 acute effect Effects 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 239000012298 atmosphere Substances 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 239000006258 conductive agent Substances 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
- 239000003792 electrolyte Substances 0.000 description 1
- 238000003912 environmental pollution Methods 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 238000005549 size reduction Methods 0.000 description 1
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- 230000009469 supplementation Effects 0.000 description 1
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Abstract
The invention discloses a lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material and a preparation method and application thereof; the composite material is obtained by heating the mixed particles of lithium phosphate and carbon nano tubes after wrapping polymers, so that the polymers are carbonized, and the lithium phosphate is converted into lithium phosphide. The mass ratio of the lithium phosphate to the carbon nano tube is 98: 2. The polymer is polydopamine. In the invention, the small-size lithium phosphide/carbon nanotube particles obtained by grinding and phosphate radical deoxidation are tightly wrapped by porous carbon, so that the electronic conductivity of the composite material is improved; meanwhile, as the lithium phosphide is tightly wrapped by the porous carbon, the separation of the lithium phosphide with unstable property from the environment is realized, the overall chemical stability of the composite material is improved, and the composite material can be applied to a hard carbon material as a lithium supplement material, and the first coulombic efficiency of the hard carbon material as a negative electrode is obviously improved.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material as well as a preparation method and application thereof.
Background
With the gradual exhaustion of fossil energy and the environmental pollution problem caused by the use of fossil energy, the utilization of renewable energy is imminent. However, renewable energy sources are characterized by instability. To make better use of it, we often need to store it. The charge-discharge battery has the function of converting electric energy into chemical energy for storage and then converting the chemical energy into electric energy for use, thereby playing an important role in the field of new energy utilization. Since the performance of the lithium ion battery approaches the theoretical limit, in order to improve the specific energy of the lithium ion battery, it is necessary to develop an electrode material with higher specific capacity. Although some novel electrode materials have higher specific capacity, the first coulombic efficiency of the novel electrode materials is too low, and the practical application is influenced. In order to improve the first coulombic efficiency, researchers have generally introduced lithium supplement materials. The lithium phosphide is expected to be a lithium supplement material due to the extremely high specific capacity (1550 mAh/g). However, its lithium supplementation application still faces some problems. On the one hand, lithium phosphide has poor electron conductivity. Also, the commercial lithium phosphide particles are too large in size to facilitate good contact of the lithium phosphide with the conductive agent, making this problem particularly acute. On the other hand, lithium phosphide is very easy to react with water vapor in air, so that further optimization (such as size reduction, carbon coating and the like) and subsequent use of the lithium phosphide material are very difficult. Therefore, a method for improving the performance of the lithium phosphide material with simple process is also required to be searched, and the application of the lithium phosphide material in the field of lithium supplement is promoted.
Disclosure of Invention
In view of the technical problems, the invention provides a lithium phosphide/carbon nanotube @ porous carbon core-shell structure and a preparation method and application thereof.
According to the first aspect, the lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material is obtained by heating mixed particles of lithium phosphate and a carbon nanotube after wrapping a polymer, so that the polymer is carbonized, and the lithium phosphate is converted into lithium phosphide.
Preferably, the mass ratio of the lithium phosphate to the carbon nanotubes is 98: 2.
Preferably, the polymer is polydopamine.
In a second aspect, the invention provides a preparation method of the lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material, which comprises the following steps:
step one, grinding lithium phosphate particles.
And step two, mixing the ground lithium phosphate particles with the carbon nano tubes to obtain the lithium phosphate/carbon nano tube material.
And step three, adding a polymer monomer and the lithium phosphate/carbon nano tube material obtained in the step two into a liquid phase system for mixing, and carrying out polymerization reaction on the polymer monomer to obtain polymer-coated lithium phosphate/carbon nano tube particles.
And step four, drying the lithium phosphate/carbon nanotube particles wrapped by the polymer obtained in the step three, heating to 600-800 ℃, and keeping for a preset time length to carbonize the polymer, so that the lithium phosphate is converted into lithium phosphide, and the lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material is obtained.
Preferably, the lithium phosphate particles in step one are prepared as follows: preparing 0.3-3M lithium chloride aqueous solution, preparing phosphoric acid solution with the concentration of the lithium chloride solution 1/3, slowly pouring the phosphoric acid solution into the lithium chloride solution, and magnetically stirring for 5 hours at normal temperature to ensure that the lithium chloride solution and the phosphoric acid solution fully react. Thereafter, lithium phosphate particles were separated by centrifugation and washed with deionized water several times.
Preferably, in the first step, the lithium phosphate particles are ground for 10 hours by a mechanical ball mill, the ball milling speed is 350r/min, and the ball-to-material ratio is 5: 1.
Preferably, in the second step, the lithium phosphate particles and the carbon nanotubes are uniformly mixed by a mechanical ball mill, the ball milling speed is 250r/min, and the ball-to-material ratio is 2: 1.
Preferably, dopamine hydrochloride is used as the polymer monomer in the third step. The reaction condition is stirring for 12 hours at normal temperature. The mass ratio of the dopamine hydrochloride to the trimethylol methylamine is 1: 1. The liquid phase system is a trihydroxymethyl methylamine water solution with the mass fraction of 1%. The mass of the trihydroxymethyl methylamine is 5-10 times of that of the lithium phosphate/carbon nanotube material.
Preferably, in the fourth step, the drying mode is drying for 12 hours in a vacuum drying oven at 100 ℃, and carrying out multiple times of alcohol washing before drying. The heating condition is that the temperature is heated to 600-800 ℃ at the heating rate of 2 ℃/min in a tube furnace in the argon atmosphere, and the temperature is naturally reduced after the temperature is maintained for 3 hours.
In a third aspect, the invention provides an application of the lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material as a negative electrode lithium supplement material.
The invention has the following beneficial effects:
1. according to the invention, firstly, the lithium phosphate is subjected to mechanical ball milling to reduce the size to 2 μm, and after the lithium phosphate reacts with the carbon material, oxygen in the lithium phosphate is removed, and the size is reduced to about 1 μm, so that the contact area of the lithium phosphate and the carbon material is increased, and the electronic conductivity of the composite material is enhanced.
2. The carbon nano tube and the polydopamine-derived carbon shell form an interwoven structure to synergistically improve the electronic conductivity of the lithium phosphide material.
3. Because the lithium phosphide is tightly wrapped by the porous carbon, the separation of the lithium phosphide with unstable property from the environment is realized, the overall chemical stability of the composite material is improved, and further the composite material can be introduced into a hard carbon material to serve as a lithium supplement material, and the first coulombic efficiency of the hard carbon material as a negative electrode is obviously improved.
4. According to the invention, lithium phosphate is converted into lithium phosphide by calcination only in the last step, and polydopamine is converted into carbon, so that the composite material of porous carbon coated lithium phosphide is obtained, and no lithium phosphide material participates in the previous steps, so that the steps required to be carried out in an inert atmosphere in the lithium phosphide preparation process are greatly reduced, the process is obviously simplified, and the cost brought by providing a drying environment for lithium phosphide is saved.
Drawings
FIG. 1 is a graph showing the charge and discharge curves of a hard carbon material at a charge and discharge rate of 0.2C when the lithium phosphide composite material prepared in example 1 of the present invention was used as a lithium supplement material.
Fig. 2 is a charge and discharge curve diagram of a hard carbon material without a lithium supplement material at a charge and discharge rate of 0.2C.
Detailed Description
In order to better explain the process and scheme of the present invention, the following invention is further described with reference to the accompanying drawings and examples. The specific embodiments described herein are merely illustrative of the invention and do not delimit the invention.
Example 1
A preparation method of a lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material comprises the following specific steps:
s1, preparing 0.3M lithium chloride aqueous solution, preparing 0.1M phosphoric acid solution, slowly pouring the phosphoric acid solution into the lithium chloride solution, and magnetically stirring for 5 hours at normal temperature to enable the two to fully react.
And S2, centrifugally separating the lithium phosphate particles generated in the step S1, washing the lithium phosphate particles for multiple times by using deionized water, and grinding the lithium phosphate particles for 10 hours by using a mechanical ball mill, wherein the ball milling speed is 350r/min, and the ball-to-material ratio is 5: 1.
And S3, uniformly mixing the lithium phosphate particles obtained in the step S2 and the carbon nano tubes through a mechanical ball mill, wherein the mass ratio of the lithium phosphate to the carbon nano tubes is 98:2, the ball milling rotating speed is 250r/min, and the ball-to-material ratio is 2: 1.
S4, adding 1% by mass of trihydroxymethyl methylamine water solution into the lithium phosphate/carbon nanotube material obtained in the step S3, uniformly stirring, then adding dopamine hydrochloride, and stirring for 12 hours at normal temperature. The mass of the trihydroxymethyl methylamine is 5 times of that of the lithium phosphate/carbon nano tube, and the mass ratio of the dopamine hydrochloride to the trihydroxymethyl methylamine is 1: 1.
And S5, centrifugally separating the lithium phosphate/carbon nano tube particles coated with the polydopamine obtained in the step S5, washing the lithium phosphate/carbon nano tube particles with alcohol for multiple times, and drying the lithium phosphate/carbon nano tube particles in a vacuum drying oven at 100 ℃ for 12 hours.
And S6, under the protection of argon (the flow is 20sccm), putting the lithium phosphate/carbon nano tube @ polydopamine obtained in the step S5 into a tube furnace, heating to 800 ℃ at the heating rate of 2 ℃/min, keeping the temperature for 3h, and naturally cooling to obtain the lithium phosphide/carbon nano tube @ porous carbon core-shell structure composite material. The composite material can be used as a lithium supplement material.
Example 2
A preparation method of a lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material comprises the following specific steps:
s1, preparing 0.9M lithium chloride aqueous solution, preparing 0.3M phosphoric acid solution, slowly pouring the phosphoric acid solution into the lithium chloride solution, and magnetically stirring for 5 hours at normal temperature to enable the two to fully react.
And S2, centrifugally separating the lithium phosphate particles generated in the step S1, washing the lithium phosphate particles for multiple times by using deionized water, and grinding the lithium phosphate particles for 10 hours by using a mechanical ball mill, wherein the ball milling speed is 350r/min, and the ball-to-material ratio is 5: 1.
And S3, uniformly mixing the lithium phosphate particles obtained in the step S2 and the carbon nano tubes through a mechanical ball mill, wherein the mass ratio of the lithium phosphate to the carbon nano tubes is 98:2, the ball milling rotating speed is 250r/min, and the ball-to-material ratio is 2: 1.
S4, adding 1% by mass of trihydroxymethyl methylamine water solution into the lithium phosphate/carbon nanotube material obtained in the step S3, uniformly stirring, then adding dopamine hydrochloride, and stirring for 12 hours at normal temperature. The mass of the trihydroxymethyl methylamine is 7 times of that of the lithium phosphate/carbon nano tube, and the mass ratio of the dopamine hydrochloride to the trihydroxymethyl methylamine is 1: 1.
And S5, centrifugally separating the lithium phosphate/carbon nano tube particles coated with the polydopamine obtained in the step S5, washing the lithium phosphate/carbon nano tube particles with alcohol for multiple times, and drying the lithium phosphate/carbon nano tube particles in a vacuum drying oven at 100 ℃ for 12 hours.
S6, under the protection of argon (the flow is 20sccm), putting the lithium phosphate/carbon nano tube @ polydopamine obtained in the step S5 into a tube furnace, heating to 600 ℃ at the heating rate of 2 ℃/min, keeping the temperature for 3h, and naturally cooling to obtain the lithium phosphide/carbon nano tube @ porous carbon core-shell structure composite material. The composite material can be used as a lithium supplement material.
Example 3
A preparation method of a lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material comprises the following specific steps:
s1, preparing 1.2M lithium chloride aqueous solution, preparing 0.4M phosphoric acid solution, slowly pouring the phosphoric acid solution into the lithium chloride solution, and magnetically stirring for 5 hours at normal temperature to enable the two to fully react.
And S2, centrifugally separating the lithium phosphate particles generated in the step S1, washing the lithium phosphate particles for multiple times by using deionized water, and grinding the lithium phosphate particles for 10 hours by using a mechanical ball mill, wherein the ball milling speed is 350r/min, and the ball-to-material ratio is 5: 1.
And S3, uniformly mixing the lithium phosphate particles obtained in the step S2 and the carbon nano tubes through a mechanical ball mill, wherein the mass ratio of the lithium phosphate to the carbon nano tubes is 98:2, the ball milling rotating speed is 250r/min, and the ball-to-material ratio is 2: 1.
S4, adding 1% by mass of trihydroxymethyl methylamine water solution into the lithium phosphate/carbon nanotube material obtained in the step S3, uniformly stirring, then adding dopamine hydrochloride, and stirring for 12 hours at normal temperature. The mass of the trihydroxymethyl methylamine is 8 times of that of the lithium phosphate/carbon nano tube, and the mass ratio of the dopamine hydrochloride to the trihydroxymethyl methylamine is 1: 1.
And S5, centrifugally separating the lithium phosphate/carbon nano tube particles coated with the polydopamine obtained in the step S5, washing the lithium phosphate/carbon nano tube particles with alcohol for multiple times, and drying the lithium phosphate/carbon nano tube particles in a vacuum drying oven at 100 ℃ for 12 hours.
S6, under the protection of argon (the flow is 20sccm), placing the lithium phosphate/carbon nano tube @ polydopamine obtained in the step S5 into a tube furnace, heating to 700 ℃ at the heating rate of 2 ℃/min, keeping the heating rate for 3h, and naturally cooling to obtain the lithium phosphide/carbon nano tube @ porous carbon core-shell structure composite material. The composite material can be used as a lithium supplement material.
Example 4
A preparation method of a lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material comprises the following specific steps:
s1, preparing 1.5M lithium chloride aqueous solution, preparing 0.5M phosphoric acid solution, slowly pouring the phosphoric acid solution into the lithium chloride solution, and magnetically stirring for 5 hours at normal temperature to enable the two to fully react.
And S2, centrifugally separating the lithium phosphate particles generated in the step S1, washing the lithium phosphate particles for multiple times by using deionized water, and grinding the lithium phosphate particles for 10 hours by using a mechanical ball mill, wherein the ball milling speed is 350r/min, and the ball-to-material ratio is 5: 1.
And S3, uniformly mixing the lithium phosphate particles obtained in the step S2 and the carbon nano tubes through a mechanical ball mill, wherein the mass ratio of the lithium phosphate to the carbon nano tubes is 98:2, the ball milling rotating speed is 250r/min, and the ball-to-material ratio is 2: 1.
S4, adding 1% by mass of trihydroxymethyl methylamine water solution into the lithium phosphate/carbon nanotube material obtained in the step S3, uniformly stirring, then adding dopamine hydrochloride, and stirring for 12 hours at normal temperature. The mass of the trihydroxymethyl methylamine is 10 times of that of the lithium phosphate/carbon nano tube, and the mass ratio of the dopamine hydrochloride to the trihydroxymethyl methylamine is 1: 1.
And S5, centrifugally separating the lithium phosphate/carbon nano tube particles coated with the polydopamine obtained in the step S5, washing the lithium phosphate/carbon nano tube particles with alcohol for multiple times, and drying the lithium phosphate/carbon nano tube particles in a vacuum drying oven at 100 ℃ for 12 hours.
S6, under the protection of argon (the flow is 20sccm), placing the lithium phosphate/carbon nano tube @ polydopamine obtained in the step S5 into a tube furnace, heating to 700 ℃ at the heating rate of 2 ℃/min, keeping the heating rate for 3h, and naturally cooling to obtain the lithium phosphide/carbon nano tube @ porous carbon core-shell structure composite material. The composite material can be used as a lithium supplement material.
Example 5
A preparation method of a lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material comprises the following specific steps:
s1, preparing 3M lithium chloride aqueous solution, preparing 1M phosphoric acid solution, slowly pouring the phosphoric acid solution into the lithium chloride solution, and magnetically stirring for 5 hours at normal temperature to enable the two to fully react.
And S2, centrifugally separating the lithium phosphate particles generated in the step S1, washing the lithium phosphate particles for multiple times by using deionized water, and grinding the lithium phosphate particles for 10 hours by using a mechanical ball mill, wherein the ball milling speed is 350r/min, and the ball-to-material ratio is 5: 1.
And S3, uniformly mixing the lithium phosphate particles obtained in the step S2 and the carbon nano tubes through a mechanical ball mill, wherein the mass ratio of the lithium phosphate to the carbon nano tubes is 98:2, the ball milling rotating speed is 250r/min, and the ball-to-material ratio is 2: 1.
S4, adding 1% by mass of trihydroxymethyl methylamine water solution into the lithium phosphate/carbon nanotube material obtained in the step S3, uniformly stirring, then adding dopamine hydrochloride, and stirring for 12 hours at normal temperature. The mass of the trihydroxymethyl methylamine is 9 times of that of the lithium phosphate/carbon nano tube, and the mass ratio of the dopamine hydrochloride to the trihydroxymethyl methylamine is 1: 1.
And S5, centrifugally separating the lithium phosphate/carbon nano tube particles coated with the polydopamine obtained in the step S5, washing the lithium phosphate/carbon nano tube particles with alcohol for multiple times, and drying the lithium phosphate/carbon nano tube particles in a vacuum drying oven at 100 ℃ for 12 hours.
And S6, under the protection of argon (the flow is 20sccm), putting the lithium phosphate/carbon nano tube @ polydopamine obtained in the step S5 into a tube furnace, heating to 800 ℃ at the heating rate of 2 ℃/min, keeping the temperature for 3h, and naturally cooling to obtain the lithium phosphide/carbon nano tube @ porous carbon core-shell structure composite material. The composite material can be used as a lithium supplement material.
When the composite material obtained in example 1 was used as a lithium supplement material, the charge/discharge curve of the negative electrode was as shown in fig. 1. The charge/discharge curve of the negative electrode to which no lithium supplement material was added is shown in fig. 2. As can be seen from the comparison, in the case of using the composite material obtained in example 1 as a lithium supplement material, the first coulombic efficiency can be calculated to be 95%. Without the use of a lithium-supplementing material, the first coulombic efficiency can be calculated to be only 64%. Therefore, the first coulombic efficiency of the negative electrode can be obviously improved by using the lithium supplement material.
The process of testing the coulombic efficiency for the first time is as follows: the performance of the lithium phosphide composite material when used for lithium supplement was tested by using a half cell. The positive electrode is made of a hard carbon material, a lithium phosphide composite material, a single-walled carbon nanotube and polyvinylidene fluoride, the hard carbon material, the lithium phosphide composite material, the single-walled carbon nanotube and the polyvinylidene fluoride are uniformly mixed in N-methyl pyrrolidone according to the mass ratio of 94:3:1:2, and are coated on a copper foil, and then the copper foil is dried in a vacuum drying oven for 12 hours at the temperature of 80 ℃. The negative electrode is a lithium sheet, Celgard2325 is used as a diaphragm, LiPF6 with the electrolyte of 1M is dissolved in a solution of ethylene carbonate, diethyl carbonate and dimethyl carbonate, and the battery is assembled by using an LIR2032 coin-shaped battery case in a glove box which is filled with argon gas for protection and has the humidity and oxygen concentration lower than 1 ppm. In the charge and discharge test system, the charge and discharge test voltage is 0.01-2V.
The above description of the embodiments is only intended to facilitate the understanding of the method of the invention and its core idea. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (10)
1. A lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material is characterized in that: the polymer is carbonized through heating the mixed particles of the lithium phosphate and the carbon nano tubes after the polymer is wrapped, and the lithium phosphate is converted into lithium phosphide.
2. The lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material as claimed in claim 1, which is characterized in that: the mass ratio of the lithium phosphate to the carbon nano tube is 98: 2.
3. The lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material as claimed in claim 1, which is characterized in that: the polymer is polydopamine.
4. The preparation method of the lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material as claimed in claim 1, wherein the preparation method comprises the following steps: grinding lithium phosphate particles;
mixing the ground lithium phosphate particles with the carbon nano tubes to obtain a lithium phosphate/carbon nano tube material;
adding a polymer monomer and the lithium phosphate/carbon nanotube material obtained in the step two into a liquid phase system, mixing, and carrying out polymerization reaction on the polymer monomer to obtain polymer-coated lithium phosphate/carbon nanotube particles;
and step four, drying the lithium phosphate/carbon nanotube particles wrapped by the polymer obtained in the step three, heating to 600-800 ℃, and keeping for a preset time length to carbonize the polymer, so that the lithium phosphate is converted into lithium phosphide, and the lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material is obtained.
5. The method of claim 4, wherein: the preparation process of the lithium phosphate particles in the first step is as follows: preparing 0.3-3M lithium chloride aqueous solution, preparing phosphoric acid solution with the concentration of the lithium chloride solution 1/3, slowly pouring the phosphoric acid solution into the lithium chloride solution, and magnetically stirring for 5 hours at normal temperature to ensure that the lithium chloride solution and the phosphoric acid solution fully react; thereafter, lithium phosphate particles were separated by centrifugation and washed with deionized water several times.
6. The method of claim 4, wherein: in the first step, the lithium phosphate particles are ground for 10 hours by a mechanical ball mill, the ball milling speed is 350r/min, and the ball-to-material ratio is 5: 1.
7. The method of claim 4, wherein: in the second step, the lithium phosphate particles and the carbon nano tubes are uniformly mixed by a mechanical ball mill, the ball milling speed is 250r/min, and the ball-to-material ratio is 2: 1.
8. The method of claim 4, wherein: in the third step, dopamine hydrochloride is adopted as a polymer monomer; the reaction condition is stirring for 12 hours at normal temperature; the mass ratio of the dopamine hydrochloride to the trimethylol methylamine is 1: 1; the liquid phase system is a trihydroxymethyl methylamine water solution with the mass fraction of 1 percent; the mass of the trihydroxymethyl methylamine is 5-10 times of that of the lithium phosphate/carbon nanotube material.
9. The method of claim 4, wherein: in the fourth step, the drying mode is drying for 12 hours in a vacuum drying oven at 100 ℃, and carrying out multiple times of alcohol cleaning before drying; the heating condition is that the temperature is heated to 600-800 ℃ at the heating rate of 2 ℃/min in a tube furnace in the argon atmosphere, and the temperature is naturally reduced after the temperature is maintained for 3 hours.
10. The application of the lithium phosphide/carbon nanotube @ porous carbon core-shell structure composite material as a lithium supplement material according to claim 1.
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